1. Field of the Invention
This invention relates in general to subsea well installations and in particular to a method of managing production from a plurality of subsea wells.
2. Background of the Invention
In a subsea oil field it is common practice to drill a plurality or cluster of subsea wells for the more efficient production of well fluid from an oil field. The well fluid typically contains water, hydrocarbon gas (gas), and hydrocarbon liquid (oil). A subsea collection manifold is sometimes used to collect the well fluid from each of the plurality of subsea wells rather than transporting the well fluid from each of the individual wells to the surface. From the collection manifold, a common riser can transport the well fluid from all of the subsea wells to a vessel at the surface of the sea.
In other situations, a riser extends from each subsea well to a vessel or platform at the surface. The well fluid from each of the wells is then transported through a common conduit to a floating production storage and offloading (FPSO) vessel located away from the platform. In this situation, the well fluid from each of the subsea wells commingle in a collection manifold located topside, on the platform, and are then pumped down to the FPSO. The conduit typically extends from the platform, along the subsea surface, and then back up to the FPSO.
In both situations, the well fluid from each of the subsea wells are commingled in a collection manifold, and then conveyed through a common riser or conduit. When multiple inflows are merged into a smaller number of outflows at a commingling point in a converging production network, the resulting mixing temperature and mixing watercut or water content in each outflow depend on how the inflows are combined. An optimum or desired combination is sometimes determined by mixing temperatures and/or water cuts. For example, an optimum or desired combination could be one that gives the highest mixing temperature in the coldest outflow in order to minimize wax or hydrate problems, or one that ensures a water cut far away from the inversion point in each outflow in order to minimize emulsion problems. In other words, in various situations, the desired or optimized mixing temperature and water content of the mixing well fluid can vary based on the situation, and the operating conditions.
The number of possible combinations can be extremely large. With n inflows and k outflows, where each inflow can be routed to any outflow, the total number N of possible combinations is given asN=kn
For example, with 20 inflows and 4 outflows, there are more than a trillion combinations. Trying to optimize the commingling by trial and error or offline hand calculations can therefore be cumbersome. Furthermore, flow conditions change continuously and offline calculations based on flow rates measured in the last well tests might become inaccurate, in particular if key events, like water breakthrough, have occurred after the last well tests.